Fluid pressure motor comprising relatively extensible and contractible piston and cylinder elements



Aug. 25, 1953 H. B. CALDWELL ETAL FLUID PRESSURE MOTOR COMPRISING RELATIVELY EXTENSIBLE AND CONTRACTIBLE PISTON Filed Aug. 9. 1948 AND CYLINDER ELEMENTS 3" Sheets-Sheet 1 3 Sheets-Sheet 2 Aug. 25, 1953 H. B. CALDWELL ETAL FLUID PRESSURE MOTOR COMPRISING RELATIVELY- EXTENSIBLE AND CONTRACTIBLE PISTON AND CYLINDER ELEMENTS Filed Aug. 9, 1948 M u ,0, w 0% EH w M N #7. N\ ww W Q W @w. A w Q ,h @L y v N\\ M Q Aug. 25, 1953 H. B. CALDWELL ETAL 2,649,842 FLUID PRESSURE MOTOR COMPRISING RELATIVELY EXTENSIBLE AND CONTRACTIBLE PISTON AND CYLINDER ELEMENTS Filed Aug. 9, 1948 s Sheets-Sheet s ZLI/ Patented Aug. 25, 1953 FLUID PRESSURE MOTOR COMPRISING RELATIVELY EXTENSIBLE AND CON- TRACTIBLE PISTON AND CYLINDER ELEMENTS Harry Balshaw Caldwell, 'Penketh, Warrington, and Kenneth George Hancock, Great Sankey, near Warrington, England, assignors to Electro-Hydraulics Limited, Warrington, England, a company of Great Britain Application August 9, 1948, Serial No. 43,306 In Great Britain May 16, 1947 This invention relates to fluid pressure operated motors comprising relatively extensible and contractible piston and cylinder elements including hydraulically or pneumatically operated motors suitable for use with retractable undercarriages, flaps, bomb doors, undercarriage doors, radiator shutters and other components in aircraft. The object of this invention is to provide a means of limiting the compression or tension effort which such a motor can exert over the last movement of travel to the extended or closed position, but which will allow the motor to exert its greatest efiort, if required, during the other part of its travel; the invention is thus particularly applicable when the object, which the motor moves, comes to rest against external stops before the motor has been fully extended or closed, so that the full eifort, which the motor is capable of exerting, is not applied by the motor as a strut or tension effort nor to the various attachments and stops which would otherwise necessitate an exceptionally strong construction to withstand such loads.

A pressure operated motor according to the present invention for moving an object from one position of rest to another against external stops comprises a cylinder and piston so formed that the effective pressure-operative area of the piston is greater during the major portion of its movement than when it approaches the end of its travel, when the object is about to contact one of the stops.

In order to obtain the greater efiective pressure operative area of the piston during the major portion of its movement the cylinder may be provided internally with a sleeve free to slide within the cylinder and formed with two abutment surfaces between which the piston can move, so that at the ends of movement of the piston the pressure operative area is provided by the annular or smaller piston face, thus limiting the compression and tension effort which the motor can exert.

In an alternative form the cylinder may be provided with an auxiliary piston rod member provided with stops, the cylinder and piston rod member being capable of relative movement between said stops and forming thepressure operative area as the piston approaches the end of its travel to limit the compression effort which the motor can exert. v

Various forms of the invention are illustrated diagrammatically in the accompanying drawings in which Figure 1 is a longitudinal section of one form. Figure 2 shows an alternative form in 3 Claims. (Cl. 12144) longitudinal section, whilst Figures 2A and 2B are detail views thereof. Figures 3, 4, 5 and 6 are sectional views of othermodified forms and Figure 6A a detail view of part of Figure 6.

Referring to the drawings, in Figure 1 is shown a construction in which the motor comprises a cylinder I60, provided with two internal ring faces or flanges 20!, 202, the cylinder being pivotally attached to a fixed point. Arranged within the cylinder is a main piston I05, slidably mounted on an extension liltb of a piston rod I06. The latter passes out throughthe end of the cylinder remote from that pivotally attached to a fixed point, the piston rod being attached to the object to be moved. The piston rod extension l06b is formed with two abutments H0 and III which limit the travel of the piston I05 on the piston rod extension. Suitable seals are provided on the piston I05, so that fluid cannot pass from one side to the other, and at the piston rod end of the cylinder, so that fluid cannot escape to atmosphere. The cylinder is provided with two connections I01, I08 through either of which fluid under pressure may be supplied to the cylinder;

In order to extend the piston and cylinder assembly, fluid under pressure through the connection iii! to the cylinder, which pressure acts on the effective area of the abutment l l l which may be regarded as an auxiliary piston and on the main piston to cause the piston and piston rod to be moved together until the piston I05 abuts againstthe ring 202, and so reaches the end of its travel. The arrangement is such that before the piston rod I06 reaches that intermediate point in its total travel at which the piston I05 reaches the end of its travel, the motor is allowed to exert its greatest effort, if required. Thereafter the auxiliary piston H l moves relatively to the piston I05, so that the last part of the travel of the piston rod I06 is accomplished by fluid pressure acting only on the area of the abutment III, which is less than the operative area of the piston I05. Movement of the piston rod-E06 continues until it comes to rest against an external stop which may, for example, be a radius arm which is locked when the piston rod reaches its full travel, that is to say, a down-lock. The areas of the main piston I05 and piston rod H16 and abutment surfaces H0 and Ill may be so arranged that the effort exerted by the motor whilst the auxiliary piston Ill and piston rod it are moving relatively to the piston [B5 is reduced to any convenient value. By this arrangement the compression effort is admittedv which the motor can exert over the last movement of travel to the extended position is limited or reduced.

The piston rod I06 may be returned or retracted by applying fluid pressure through the connection I08 at the opposite end of the cylinder, so that the piston rod I and piston I move together until the piston I05 contacts the other ring 20] in the cylinder.

Referring now to the arrangement shown in Figures 2, 2A and 213, this is a construction similar to Figure 1 but is adapted for operation in one direction, that is to say for extension, by an alternative source of pressure supply. In Figures 2, 2A and 2B the cylinder I00 contains a reciprocable floating sleeve IOI within which a piston I05 is slidably arranged. The piston I05 carries a piston rod IEEA which extends outwardly through one end of the cylinder I00 and is provided with a fluid connection II2 which permits access of fluid under pressure from one source to the interior of the cylinder to cause extension of the motor. At the other end of the cylinder from the piston rod I06A there is provided another connection I07 by which fluid under pressure may be admitted from another source. Slidably arranged in the cylinder I05 between the connection I07 and the sleeve MI is a floating sleeve H3 in which there is slidably mounted for reciprocation an auxiliary floating piston H4.

The position of the moving parts when the piston rod I06A is retracted is shown in Figure 2A. When fluid under pressure is admitted through connection It]? to extend the motor the floating sleeve I I3 will move with respect to the cylinder I00 and the auxiliary piston H4 and carry with it the floating sleeve I0! so that the latter slides in respect to the cylinder I00 and the piston I05. This movement will continue until contact is made between the floating sleeve I I3 and the stop on the inner end of the floating piston I I4, or between the stop I02. on the sleeve NH and the piston I05 whichever occurs first (see Figure 2B). Thereafter parts H3, H4, IOI and I05 move together with pressure acting on the full area, of the cylinder bore until, after a predetermined amount of extension, the sleeve IIII comes to a stop, thus bringing to a stop the floating sleeve I I3. Fluid pressure will now move the floating piston M4 to slide further to the right (see Figures 2A and 23), carrying the piston I05 with it after contact has been made; thus over the last part of the extension of the motor piston, pressure is acting on the area of the floating piston [I4 only, and over the other part, on the travel of the combined area of the floating piston H4 and floating sleeve II3, that is the area of the cylinder bore. When fluid pressure is applied through the connection II2 to extend the piston, or, through connection I08, to retract the piston, the motor works in the manner described with reference to Figure 1.

Referring to the arrangement shown in Figure. 3 the motor consists of a cylinder II5 divided will act on the floating pistons I23 and I24 simul taneously. Fluid can also be admitted through connections II? and I19 and through a connec tion I26 which passes through the piston rod I2I of the piston I22 so as to enter the bore of the cylinder II5. The fluid connections H9 and I20 are coupled together so that fluid pressure is admitted and exhausted simultaneously at both connections.

When fluid pressure is admitted at II'I, the cylinder H5 will move initially relatively to the aum'liary piston I until the stop I2'I is reached by the auxiliary piston I25; then the piston I22 will move leftwards into the cylinder until it comes to a stop against the floating piston I23, which abuts against the diaphragm I I6; the fluid pressure will then move the cylinder and with it the piston I22 relatively to the auxiliary piston I25 until the latter contacts stop I28.

To extend the piston, fluid pressure is admitted simultaneously through the connections H9 and I20. Pressure through the connection I20 passes through the bore of the piston rod I2I and piston E22 to move the sliding piston assembly to the right, fluid behind the piston being exhausted through connection II'I. At the same time fluid pressure through the connection H9 will act on the auxiliary piston I25. But to external load and the small area of the piston I25 the said piston will be held onto the stop I28 until the outward movement of the piston I22 comes to a pre-determined stop. Further extension of the motor with a smaller load will then be eflected by the travel of the auxiliary piston I25 between the stops I23 and I21,

Fluid pressure from another source of supply can be admitted at connection IIB to extend the motor. This pressure will act simultaneously on the floating pistons, I23 and I24. The floating piston I 23 will carry the piston assembly ,I2I and I22 with it, and the floating piston I24 will move the auxiliary piston I25 from the stop I28 against the stop I21. It will be appreciated that chamber A comprises the closing and'retracting part of the motor, and chamber B the load limiting part, also that the alternative source of supply provides in some cases fluid under a lower pressure than the normal supply so that it is not necessary to extend the motor with a load limiting device. 7

Thus should load limiting be desired for extension with normal and alternative pressures, the diameter of the chamber B can be made smaller than the diameter of the chamber A, the diaphragm III; thus abutting against a shoulder formed between the difierence in diameters so that when fluid pressure is admitted at I it it will act on the floating piston I23 carrying the floating piston assembly, until it reaches a pre-determined stop. Due to the smaller area this pressure acts on, the floating'piston I24 will carry the auxiliary piston I25 off its Stop after the floating piston I23 has reached its stop.

in an'alternativ'e form shown in Figure 4 the motor comprises a' cylinder I in which a piston 2 and piston rod 3 are free to slide, whilst at the end of the cylinder remote from the piston rod and passing into the cylinder is an auxiliary piston ro'd'm'ember'l provided with two shoulders 5, 6 spaced'any convenient distance apart, one within and one without the cylinder, which is free to slide betweensaid shoulders. The auxiliary piston rod 4 is pivotally attached at I to a fixed point, the main, pi tonirod 3 being attached to the object'to'be moved". 'Again suitable seals are in- 'erp'bmt'ed 'to prevent leakage 6: pressure fluid from one side of the piston to the other and to prevent leakage to atmosphere between the cylinder and main piston rod and between the cylinder and the auxiliary piston'rod.

Fluid under pressure is allowed to enter the cylinder through a connection 8, which pressure causes relative movement between the auxiliary piston rod 4 and cylinder I until contact is made between the cylinder I and the external stop 5 on the auxiliary piston rod provided that the cylinder is not already in this position. Thereafter pressure acts on the full area of the main piston 2 producing a force which extends the motor, until the main piston abuts against a stop I I in the remote end of the cylinder during which time the piston rod 3 has moved from its initial point A to an intermediate point C of its travel approaching the end thereof. The final movement of the piston rod from C to B is eflected by fluid pressure acting between the cylinder I and auxiliary piston rod 4 causing the cylinder to slide with respect thereto until it approaches or contacts the inner stop 6 on the auxiliary piston rod, at which time the motor becomes fully extended so that during the last movement of travel to the extended position the compression effort which the motor can exert is limited. If desired to return the piston, fluid pressure may be applied through a connection 9.

In another alternative form illustrated in Figure 5 the cylinder I is provided with an ex-' ternal shoulder l5 sliding within an end fitting including a hollow auxiliary piston rod l6 provided with two abutment surfaces [1, I8, limiting the relative movement between the cylinder I and the auxiliary piston rod I6. The end of the cylinder which slides in the end fitting comprising the auxiliary piston rod is closed except for a small hole I9 which permits fluid under pressure to enter the annular space between the cylinder and the abutment surfaces, whilst suitable sealing rings are provided so that leakage cannot occur from this annular space, suitable breathing holes 23, 24 being provided so that air is not trapped in the spaces 2 I, 22. Again suitable sealing rings are incorported on the piston so that fluid cannot flow from one side to the other, and on the piston rod end of the cylinder so that fluid cannot leak to atmosphere.

Hydraulic pressure is applied at connection 25, which by acting on the full area of piston 2 produces a force which extends the piston. At the instant pressure is applied at connection 25, the cylinder slides in the end fitting I6 until the shoulder I8 on the end fitting is in contact with the shoulder I5, provided that the shoulders are not already in contact. It is arranged that when the piston rod has moved from point A to some intermediate point C, the piston 2 meets the stop I I on the cylinder, and thereafter movementv from C to B is accomplished by hydraulic pressure acting on the annular area of the shoulder I5, the cylinder I, piston 2 and piston rod 3 moving together. 7

In a further modified form as shown in Figures 6 and 6A the motor comprises a cylinder 38 in which a piston 39 and a hollow piston rod 40 are free to slide. The cylinder 38 is closed at one end by an end fitting 42 through which the piston rod 41) slides. At its other end it is closed by an end fitting 4i which constitutes an extension of the cylinder, and has a bore in which an auxiliary piston 49 is free to slide. The auxiliary piston has fixed thereto at one end an attachment The stroke of the auxiliary piston 46 is limited by shoulders 44, 45 as illustrated in Figure 6, or by shoulder 45 and a shoulder 44a on the eyebolt, as shown in Figure 6A. A pressure fluid connected 48 is provided in the end fitting 42, whilst there is also a pressure fluid connection3'I in the end fitting 4|. A main piston 39 carried by the hollow piston rod 40 slides. in the cylinder 38. The end fitting 42 also provides a stop 41 for limiting the outward movement of the piston rod 40 and piston 99 carriedithereby.

On application of pressure fluid through connection 3?, the cylinder 38 moves first to the left until contact is made between the abutment 44 and the auxiliary piston 46, provided such con- .tactis not existing already. The pressure acting on the annular area of the piston 39 then forces it andthe piston rod 40 to the right, producing the maximum effort and extending the piston rod 49. After the piston rod 49 has moved from its initial point A (its closed position) to an intermediate point C, the main piston 39 contacts the stop 47 at the end of the cylinder, and the final extending movement of the piston rod 40 to point B is accomplished by pressure fluid moving the cylinder 38, piston 39 and rod 40 to the right until the auxiliary piston 46 contacts the stop 45. The piston rod 49 may also be extended by admission of fluid pressure, preferably from another source of fluid pressure at the opening 36. Pressure fluid will then pass through the bore of the auxiliary piston 46, the bore of tube 43, and the bore of piston rod 40 to extend the latter.

The piston rod 40 can be retracted by supplying pressure fluid through the connection 48 so as to act on the annular area of the piston 39 to move it and the piston rod 40 to the left.

Figure 6A diifers only from Figure 6 in that the position of the stop which limits movement of auxiliary piston 46 in one direction is changed from a shoulder 44 on the end fitting 4| to a shoulder 44a on the eyebolt; apart from this there is no functional difference.

What we claim is:

1. In a fluid pressure motor, a cylinder; a first piston reoiprocable therein; a piston rod fast with said first piston and extending through one end of said cylinder; a cylinder part at the opposite end of said cylinder of smaller diameter than the cylinder part in which said first piston is reciprocable; a second piston 'reciprocable in said smaller diameter cylinder part; abutments for limiting the reciprocation of said second piston relative to said cylinder; an apertured partition on said cylinder between said first and second pistons, the diameter of said cylinder between said partition and said second piston being greater than the diameter of said cylinder between said partition and said first piston; a first floating piston reciprocable in said cylinder between said partition and said first piston; a second floating piston reciprocable in said cylinder between said partition and said second piston; and means for admitting pressure fluid to and discharging it from the spaces respectively between said first piston and the adjacent end of the cylinder, between said first piston and said first floating piston, between said first floating piston and said partition, and between said second piston and said second floating piston.

2. In a fluid pressure motor, a cylinder; a first piston reciprocable therein; a hollow piston rod fast with said first piston and extending through one end of said cylinder; separate means for admitting pressure fluid to and discharging it from said cylinder between said first piston and the respective ends of said cylinder; a reduced diameter cylinder portion at the opposite end of said cylinder; shoulders at the opposite ends of said cylinder portion; a second and hollow piston reoiprocable in said cylinder portion within limits determined by said shoulders and having a part extending through the outer end of said cylinder portion; a tube fast with said second piston and extending through said cylinder and slidable through said first piston and communicating with the interior of said second piston and with said hollow piston rod; and means for admitting pressure fluid to and discharging it from said hollow piston.

3. In a fluid pressure motor, a cylinder; a main piston relatively reciprocable in said cylinder having a rod extending through one end to the outside thereof; an auxiliary piston reciprocable relatively to both said cylinder and said main piston and being spaced from said main piston longitudinally of said cylinder, said main and auxiliary pistons having different effective areas exposed for action thereon by fluid pressure in said cylinder and being movable by said pressure in opposite directions; means for transmittting short due to relative movement of said cylinder and opposite direction movements of said pistons; and means for limiting movement of one of said pistons relatively to said cylinder before the end of the coacting movement of the other piston so that when said one of said pistons is stopped by said limiting means, the other of said pistons will continue its movement in deceleration of the stroke while exerting an efiort different from the effort exerted prior to stopping of said one of said pistons.

HARRY BALSHAW CALDWELL.

KENNETH GEORGE HANCOCK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 787,479 Tanner Apr. 18, 1905 787,480 Tanner Apr. 18, 1905 2,259,576 MacMillin Oct. 21, 1941 2,464,962 Bent Mar. 22, 1949 2,485,805 Bent Oct. 25, 1949 FOREIGN PATENTS Number Country Date 679,260 Germany Aug. 1, 1939 

